This invention relates to a dynamic calibration monitor and feedback regulator for monitoring and regulating the high voltage applied to an ionization detector. This invention is useful for any ionization radiation detector system where precise operational setpoints for the detector is regulated. More particularly, the present invention relates to a dynamic calibration monitor and feedback regulator utilizing a three terminal floating voltage regulator and an adjustable calibration display to provide visual indication and automatic control of present calibration status relative to the original calibration setpoint.
Ionization tube detectors are typically powered using an unregulated high voltage power supply. However, the output voltage of an unregulated power supply can change substantially with changes in the load. The tube and the power supply form a coupled system in which physical changes in the tube result, in many cases, in changes in power supply loading with a corresponding change in output voltage. Examples of such physical changes include molecular leaks in the tube envelope, damage by dust or vibration (including noise), and overall aging.
The sensitivity of an ionization tube radiation detector is directly related to its powering voltage. Therefore, physical changes in the tube and their corresponding loading and voltage changes will directly affect detector sensitivity. In many applications, changes in detector sensitivity must be minimized, so that some form of voltage calibration and monitoring is needed. Further, a limited amount of feedback control is desirable for automatically correcting small variations in powering voltage. Thus, a device is needed to monitor the calibration changes over the life of the tube and to regulate the voltage with changes in loading.
Ionization tube detectors are highly nonlinear. When unregulated voltage is used to power the detector, variations in this powering voltage produces nonlinear variations in the detector output voltage. For example, if an open loop, no feedback, high voltage power supply is used to power an ionization detector, variations in the DC power supplied to the high voltage power supply and variations in the load regulation of the high voltage power supply produce non-linear changes in the detector output. As an example, when a high voltage inverter transformer from Pulse Engineering, P.0. Box 12235, San Diego, Calif. is used to power the detector, the detector is subjected to the inventer's 15% load regulation range.
If an ionization detector with an unregulated power supply is used to monitor cigarette production, then measurements made by the detector will be subject to errors due to variations in the output voltage of the high voltage power supply. Measurement errors can lead to increased tobacco costs in the manufacture of cigarettes and increased maintenance costs. Variations in the powering voltage can reduce detector lifetime.
In view of the foregoing, it is an object of this invention to provide a dynamic calibration monitor and feedback regulator having exceptional voltage regulation performance.
It is another object of this invention to provide a dynamic calibration monitor and feedback regulator having an adjustable calibration display for monitoring and adjusting the error voltage using feedback control.
It is a further object of this invention to provide a dynamic calibration monitor and feedback regulator having an adjustable calibration display that is easy to read and understand.
It is a still further object of this invention to provide a dynamic calibration monitor and feedback regulator that is suitable for use in a harsh production environment.
It is also an object of this invention to provide a dynamic calibration monitor and feedback regulator that supplies regulated high voltage to an ionization detector.